There is a recent trend for mobile equipment to be equipped with a small camera module. Attempts are being made to develop a further miniaturized camera module having improved and diversified capabilities.
Such capabilities include a mechanism that changes the focal length as an afocal lens (with an angular magnification smaller than 1) is attached to or detached from the subject side of the image-forming lens. This mechanism is applicable to the built-in camera in the portable telephone or computer or the monitoring camera. An example of the variable power optical system is disclosed in Japanese Patent Laid-open No. Hei-7-20367. It has an afocal system consisting of a negative lens group and a positive lens group that are placed a certain distance apart. The afocal system is held in a lens barrel which has an lateral opening. The afocal system (which is placed in front of the image-forming lens) is moved out of the optical axis as it is turned through 90°. In this state, the lateral opening in the lens barrel functions as a window that permits the image-forming lens to take a photograph by itself.
The camera module to be built into the portable equipment needs improvement in its performance without its mechanism getting complex and large and its power consumption increasing. In other words, the lens system of the camera in the portable telephone or notebook personal computer is restricted in its depth, because the camera has to fit into the thickness of the portable telephone or the thickness of the cover of the personal computer. In addition, the camera that relies on a power supply from the battery needs a means to save power consumption.